One application in which a flexible coupling is used is in interconnecting the drive shafts used in the transmission of drive to the actuators associated with aircraft flight control surfaces such as wing mounted slats and flaps.
One type of flexible coupling that is well known comprises a series of mounting fingers formed on one of the rotatable components, the fingers each defining a fixing point to which a torque transmission disc is secured. By way of example, three such fingers and fixing points may be provided. The disc is conveniently secured to the fingers using bolts or other fasteners which extend through the openings formed in the fingers, the bolts or other fasteners being secured to respective parts of the torque transmission disc. The other of the rotatable component is similarly provided with a series of mounting fingers defining a series of fixing points to which the torque transmission disc is mounted. The parts of the disc secured to the fixing points of one of the components alternate with those by which the disc is secured to the other of the components.
In use, rotation of one of the rotatable components is transmitted to the torque transmission disc, and from the torque transmission disc to the other of the rotatable components. Any slight angular misalignment of the axes of rotation of the rotatable components can be accommodated by limited flexing of the torque transmission disc.
A number of different materials and designs of torque transmission disc are known. It is desirable to use composite materials for this purpose as they may be of reduced weight compared to other materials whilst being able to transmit the required level of torque.
One disadvantage of composite material torque transmission discs is that if the disc is subject to a relatively large out of plane flexing load, such as may occur during handling or during installation, or, for example, where installed between a pair of elongate drive shafts and work is being undertaken at the other end of one of the shafts requiring movement of that shaft, the degree of flexing which may take place may result in delamination, or partial delamination, of the torque transmission disc. Such delamination or partial delamination may result in the torque transmission disc being weakened. There is a fear that such weakening may not be noticed prior to installation, or during servicing, and that an installed torque transmission disc may fail, in subsequent use. The weakening may be such that the failure may occur some time after installation. The risk of the presence of such a latent fault may, depending upon the application in which the coupling is used, be unacceptable.
U.S. Pat. No. 6,200,223 illustrates a coupling of the general type described hereinbefore and in which the means by which the torque transmission disc is secured in position are such that drive may continue to be transmitted even in the event of a failure of the torque transmission disc.
It is an object of the invention to provide a flexible torque coupling in which the risk of damage to parts of the coupling is reduced.